1. Field of the Invention
The present invention relates to calculators and apparatus for still photography. More particularly, the invention relates to a calculator and apparatus for macrophotography.
2. Description of the Prior Art
Photomacrography, macrophotography or close-up photography involves the taking of photographs with the film effectively positioned extremely close to the subject being photographed so that the size of the image on the film is approximately equal, slightly smaller, or larger than the size of the object being photographed. For instance, macrophotography involves taking pictures in which the ratio between the size of the object being photographed and the size of the image on the film (reproduction ratio) varies from approximately 1:2 to 8:1. When taking such pictures, it is common practice to use extension tubes or bellows.
As described in the book entitled "Adventures In-Slide Photography" (copyrighted by Eastman Kodak Company in 1976), one difficulty in using extension tubes or bellows is that appropriate corrections must be made to provide additional exposure in order to compensate for the changed ratio between the lens opening and the focal length. There are numerous ways to provide such compensation. For instance, page 203 of the previously cited book provides a table indicating that when the long dimension of the field size is 11 inches, the lens should be opened by 1/3 f-stop or exposure time should be multiplied by 1.3. The same table indicates that when the field size long dimension is 1 inch, the lens should be opened by 21/2 f-stops or exposure time should be multiplied by 5.7. It should be readily apparent from the preceding that appropriate compensation for use of extension tubes and bellows is critical to successful macrophotography and can be quite complex.
Macrophotography involves taking pictures in either bright sunlight or with flash illumination. When an on-camera electronic flash is used, it is necessary to reduce the amount of light to avoid over exposure of the picture. A convenient way to reduce the amount of light is to use an electronic flash having a variable power output, such as the SUNPAK AUTO 311 or 322. The 322 flash unit has the following power ratios: full, 1/2, 1/4, 1/8, 1/16, and 1/32 and includes a first set of calculation scales that interrelate film sensitivity (ASA number) with f-stop and a second set that interrelates distance with the power ratio. In use, a first button or lever is pushed to set the ASA number in a viewing window. This movement results in shifting indicia representing various f-stop values. A second button or lever is then pushed to set the power ratio. Movement of the second or lever button moves a distance scale. The user then reads an appropriate f-stop value opposite the distance. For instance, with an ASA of 100 and a full power ratio, a f-stop of 32 should be used at a distance of approximately 2.3 feet. No provision is made with the unit's calculation scales for adjusting exposure factors to compensate for the use of extension tubes or bellows. Further, the distance scale does not include the various short distances often encountered with macrophotography. Thus, it can be quite difficult to appropriately correct the exposure parameters to ensure adequate compensation for both short distances, i.e., distances of a foot or less, and for bellows extension.